use std::pin::Pin;
use std::task::{Context, Poll};

use pin_project_lite::pin_project;

pin_project! {
		/// Extends an underlying [`hyper`] I/O with [`tokio`] I/O implementations.
		///
		/// This implements [`AsyncRead`] and [`AsyncWrite`] given an inner type that implements
		/// [`Read`] and [`Write`], respectively.
		#[derive(Debug)]
		pub struct WithTokioIo<I> {
				#[pin]
				inner: I,
		}
}

// ==== impl WithTokioIo =====

/// [`WithTokioIo<I>`] is [`AsyncRead`] if `I` is [`Read`].
///
/// [`AsyncRead`]: tokio::io::AsyncRead
/// [`Read`]: hyper::rt::Read
impl<I> tokio::io::AsyncRead for WithTokioIo<I>
where
	I: hyper::rt::Read,
{
	fn poll_read(
		self: Pin<&mut Self>,
		cx: &mut Context<'_>,
		tbuf: &mut tokio::io::ReadBuf<'_>,
	) -> Poll<Result<(), std::io::Error>> {
		// let init = tbuf.initialized().len();
		let filled = tbuf.filled().len();
		let sub_filled = unsafe {
			let mut buf = hyper::rt::ReadBuf::uninit(tbuf.unfilled_mut());

			match hyper::rt::Read::poll_read(self.project().inner, cx, buf.unfilled()) {
				Poll::Ready(Ok(())) => buf.filled().len(),
				other => return other,
			}
		};

		let n_filled = filled + sub_filled;
		// At least sub_filled bytes had to have been initialized.
		let n_init = sub_filled;
		unsafe {
			tbuf.assume_init(n_init);
			tbuf.set_filled(n_filled);
		}

		Poll::Ready(Ok(()))
	}
}

/// [`WithTokioIo<I>`] is [`AsyncWrite`] if `I` is [`Write`].
///
/// [`AsyncWrite`]: tokio::io::AsyncWrite
/// [`Write`]: hyper::rt::Write
impl<I> tokio::io::AsyncWrite for WithTokioIo<I>
where
	I: hyper::rt::Write,
{
	fn poll_write(
		self: Pin<&mut Self>,
		cx: &mut Context<'_>,
		buf: &[u8],
	) -> Poll<Result<usize, std::io::Error>> {
		hyper::rt::Write::poll_write(self.project().inner, cx, buf)
	}

	fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), std::io::Error>> {
		hyper::rt::Write::poll_flush(self.project().inner, cx)
	}

	fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), std::io::Error>> {
		hyper::rt::Write::poll_shutdown(self.project().inner, cx)
	}

	fn is_write_vectored(&self) -> bool {
		hyper::rt::Write::is_write_vectored(&self.inner)
	}

	fn poll_write_vectored(
		self: Pin<&mut Self>,
		cx: &mut Context<'_>,
		bufs: &[std::io::IoSlice<'_>],
	) -> Poll<Result<usize, std::io::Error>> {
		hyper::rt::Write::poll_write_vectored(self.project().inner, cx, bufs)
	}
}

/// [`WithTokioIo<I>`] exposes its inner `I`'s [`Write`] implementation.
///
/// [`Write`]: hyper::rt::Write
impl<I> hyper::rt::Write for WithTokioIo<I>
where
	I: hyper::rt::Write,
{
	#[inline]
	fn poll_write(
		self: Pin<&mut Self>,
		cx: &mut Context<'_>,
		buf: &[u8],
	) -> Poll<Result<usize, std::io::Error>> {
		self.project().inner.poll_write(cx, buf)
	}

	#[inline]
	fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), std::io::Error>> {
		self.project().inner.poll_flush(cx)
	}

	#[inline]
	fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), std::io::Error>> {
		self.project().inner.poll_shutdown(cx)
	}

	#[inline]
	fn is_write_vectored(&self) -> bool {
		self.inner.is_write_vectored()
	}

	#[inline]
	fn poll_write_vectored(
		self: Pin<&mut Self>,
		cx: &mut Context<'_>,
		bufs: &[std::io::IoSlice<'_>],
	) -> Poll<Result<usize, std::io::Error>> {
		self.project().inner.poll_write_vectored(cx, bufs)
	}
}

impl<I> WithTokioIo<I> {
	/// Wraps the inner I/O in an [`WithTokioIo<I>`]
	pub fn new(inner: I) -> Self {
		Self { inner }
	}

	/// Returns a reference to the inner type.
	pub fn inner(&self) -> &I {
		&self.inner
	}

	/// Returns a mutable reference to the inner type.
	pub fn inner_mut(&mut self) -> &mut I {
		&mut self.inner
	}

	/// Consumes this wrapper and returns the inner type.
	pub fn into_inner(self) -> I {
		self.inner
	}
}

/// [`WithTokioIo<I>`] exposes its inner `I`'s [`Read`] implementation.
///
/// [`Read`]: hyper::rt::Read
impl<I> hyper::rt::Read for WithTokioIo<I>
where
	I: hyper::rt::Read,
{
	#[inline]
	fn poll_read(
		self: Pin<&mut Self>,
		cx: &mut Context<'_>,
		buf: hyper::rt::ReadBufCursor<'_>,
	) -> Poll<Result<(), std::io::Error>> {
		self.project().inner.poll_read(cx, buf)
	}
}
